This invention relates to a vertical heat treating device, especially to a boat loader for use in vertical heat treating devices for diffusion, oxidation, annealing and film forming treatment.
In general, a boat (the so-called wafer boat) for batch-treating a plurality of objects to be treated, such as semiconductor wafers, in heat treatment steps is provided in, e.g., a vertical reaction furnace, in a treatment chamber of a vertical heat treating device, and a boat loader for loading and unloading the boat into and out of the reaction furnace is provided.
Some requirements of the boat for the batch treatment of the objects to be treated are not only that the boat can mount a number of objects to be treated, but also that a procedure for loading the boat into the reaction furnace is efficient to improve the so-called throughputs of the heat treating device.
To this end, it is proposed that a boat with a next set of objects to be treated mounted thereon stands by to be loaded into the reaction furnace while the heat treatment is going on objects-to-be-treated mounted on another boat, and when the heat treatment is over, the latter boat is immediately replaced by the former boat to continuously conduct the heat treatment on the objects to be treated on the loaded boat. This structure is called a two boat system which includes in the treatment chamber a place where a boat to be next treated waits, and a place where a heat-treated boat unloaded from the reaction furnace waits.
One of the boat loaders which use the two-boat system includes boat mounts provided on both ends of a rotary arm, and the mounts are rotated by 180.degree. between a lower position of a boat elevator and a position where a boat with objects-to-be-treated mounted thereon for a next heat treatment waits, whereby the boats are loaded into the reaction furnace (See e.g., Japanese Patent Laid-Open Publication No. 291335/1986). Another boat loader includes a swingable cantilever arm instead of the boat mounts on both ends of the arm as described above, whereby the arm is swung between a new boat loading position and a position where the treated boat waits, and the treated objects on the boat unloaded out of the reaction furnace are transferred on a swing path (See e.g., Japanese Patent Application No. 82521/1990, which is one of the applications of the applicant of the present application).
But the above-described boat loader needs a set rotation radius of the arm, and the arm tends to occupy a large space in the treatment chamber. Accordingly problems are encountered in that the vertical heat treating device cannot be smaller-sized, and its structure is complicated.
That is, in terms of sizes of the heat treating device, a suitable gap is necessary for preventing thermal interference between a heat treated boat and a boat to be mounted on the boat elevator for a next heat treatment. There is a possibility that the arm will need a considerably large radius, and the arm adversely occupies a large space in the heat treating device.
These are obstructions when it is considered that vertical heat treating devices of this type are expected to have higher throughputs, and to this end, there is a tendency to include a larger number of reactors per an area in a clean room, whose cost per unit area is on the increase.
In terms of structures of the heat treating device, the structures have been increasingly complicated. One reason for that is the arm of a set rotation radius has an operation which does not interfere with the carrier or the boat elevator while the arm is being moved to the respective waiting positions of the boats. Another reason is that for the transfer of a boat, or the objects to be treated, the wafers, on the boat, one unit has to include shafts for rotating and lifting the boats, or the objects to be treated. In addition, to position the arm at the respective waiting positions, based on a rotation radius and a rotation angle of the arm, an allowance of the arm with respect to the lower end plate of the boats in which the arm is inserted is as small as, e.g., 0.2-0.3 mm. On the other hand, the allowance of the rotation radius or the rotation angle is not permitted to be larger, i.e., the so-called teaching of the arm for the positioning in consideration of a radius error or an angle error must be very accurate. Accordingly the teaching processing is very difficult. In addition, as the structure is complicated, more dust is generated in respective mechanisms, and the risk that the dust might stick to the wafer surfaces on the boats is higher.
The dust tends to be influenced by turbulences of air flow in the treatment chamber due to heat from the reaction furnace, and it is necessary that the influence by the turbulences of air flow be removed, and even when the turbulences occur, dust must be suppressed from sticking to the surfaces of the objects to be treated at the waiting positions.